This invention relates to phosphors emmitting visible luminescence under ultra violet excitation, and more particularly, to a cubic, yttria-stabilized HfO.sub.2 phosphor, doped with cerium.
The term phosphor is generally employed in the art to describe luminescent or fluorescent solids which are composed of two ingredients; a "host" matrix, and an "activator" impurity. Such phosphors find many diverse uses including laser applications, as fluorescent lamps, and color cathode ray tubes.
The properties of the cubic form of HfO.sub.2 phosphors are unknown since the material normally exists in its monoclinic crystalline state. The only reference in the prior art to a "probable cubic form" of HfO.sub.2 is that of L. Passerini: Gazz, Chem. Ital. 60, 762-766 (1930), who hypothesized that cubic HfO.sub.2 should have a cell edge a.sub.o =5.155 A. This value, however, was extrapolated from measurements of cubic cell-edges of the crystal HfO.sub.2 --CeO.sub.2, where samples ranging from 95 to 5% CeO.sub.2 were measured. Pure HfO.sub.2 has not been actually found to have a cubic (fluorite) structure; when fired up to 1300.degree. C. it is, as we have verified, monoclinic.